1. Field of Invention
The present invention relates in general to the field of installations for cryogenically cooling superconducting devices, and more particularly to improvements made to such installations comprising:                a tank for a two-phase cryogenic fluid in which a superconducting device to be cooled is immersed;        a cryogenic fluid supply line functionally associated with the tank in order to supply it with cryogenic fluid;        a valve for controlling the supply of cryogenic fluid, which is placed in said supply line; and        an outlet manifold connected to said tank.        
2. Description of Background Art
A conventional arrangement of an installation according to the invention is illustrated in FIG. 1 of the appended drawing. A tank 1 contains a two-phase cryogenic fluid, the liquid phase 2 of which lies beneath a vapor phase 3. A superconducting device 4 is immersed in the liquid phase 2. A cryogenic fluid supply line 5 is connected to the tank 1 and a control valve 6, incorporated in the supply line 5, allows the supply of cryogenic fluid into the tank 1 to be controlled. An outlet manifold 7 is provided for discharging the cryogenic fluid vaporized by the thermal loads of the system. Finally, the tank 1 is provided with a level gauge 8, for example functionally associated with the control valve 6, in order to detect the level to which the tank 1 is filled with cryogenic fluid in the liquid phase and for controlling the control valve 6.
The heat loads of the system are absorbed by partial vaporization of the cryogenic liquid, by playing on the latent heat of vaporization of the latter. The vaporized cryogenic fluid is discharged via the outlet manifold 7, whereas cryogenic fluid in the liquid state is supplied according to the requirements under the control of the level gauge 8 and the control valve 6, so that the superconducting device 2 always remains immersed.
However, in the presence of a resistive transition of the device or of any other thermal disturbance resulting in a large and rapid increase in the thermal load, the cryogenic fluid in the liquid state, in contact with which the device must be maintained, rapidly and completely disappears owing to its vaporization, due to the increase in thermal load, and owing to its turbulent entrainment at high flow rate in the outlet manifold. The resumption of cooling of the device and the recovery of its superconductivity state require that cryogenic fluid in the liquid state be again supplied to the tank. This new supply of liquid cryogenic fluid not only requires time, but above all requires an influx of fluid, which proves to be expensive.